Over 1000 hours of EGR operation have now been achieved aboard the Maersk Cardiff, a container newbuild from A.P. Moller-Maersk with a two-stroke MAN B&W 6S80ME-C9 engine. Having demonstrated reliable compliance with Tier III NOx legislation, as well as the potential for fuel savings in Tier II operation, the vessel’s EGR installation will soon be expanded with another remarkable technology: a pressurized EGR boiler from Alfa Laval.
“We have shown that EGR works smoothly and that it complies fully with the NOx limits appearing in 2016,” says Michael Witt, Head of Retrofit Development R&D at MAN Diesel & Turbo. “Together with Alfa Laval and A.P. Moller-Maersk, we are now looking beyond compliance to optimize the system and to utilize opportunities for energy savings.”
According to Anders Busk Nielsen, Project Manager at Alfa Laval’s Product Centre Boilers, one such opportunity is waste heat recovery. “EGR is a fantastic technology that is already well served by Alfa Laval’s separation know-how,” Nielsen says. “Now we are adding our expertise in waste heat recovery, by placing a pressurized exhaust gas boiler in the EGR circuit. If successful, it could add substantial energy savings to NOx emission compliance.”
Reclaiming the diverted waste heat
The reasons for developing an EGR boiler are straightforward. In the EGR process, around 30% of the exhaust gas is directed back into the engine, which reduces the combustion temperature and thereby the production of NOx. This also reduces waste heat recovery by 30%, since only 70% of the gas reaches the traditional exhaust gas boiler after the turbocharger. The remaining heat energy is dissipated in the EGR scrubbing process.
“The idea is to place an in-line boiler ahead of the EGR wet scrubber, before the scrubber jets cool the exhaust gas,” says Nielsen. “In this location, the boiler would have access to much higher temperatures and pressures than traditional exhaust gas boilers. That would allow a lighter and more compact boiler, which would be self-cleaning due to the high speed of flow.”
The heat would be recovered from the EGR circuit, and the availability of service steam would be unchanged from today. Moreover, as part of an integrated waste heat recovery system, the EGR boiler would enable a major increase in efficiency.
Standing up to extreme post-engine conditions
If the theory is simple, the challenges of constructing an EGR boiler are anything but. Today’s waste heat recovery involves temperatures of around 270°C, whereas temperatures before the EGR scrubber are twice that. In addition, the potential gas pressure in the EGR circuit is 2-4 bar(g), which necessitates a pressurized boiler casing.
“Managing the extreme conditions has been a real challenge for the Alfa Laval development team,” says Nielsen. “These are conditions no ordinary boiler would be able to survive. But what we’ve developed is no ordinary boiler.”
The boiler Nielsen refers to is the new Aalborg XW-HPX pressurized EGR boiler, which is indeed lighter and more compact than any boiler with an equivalent output. Tentatively planned for launch in 2015, the boiler has moved off the drawing board and is now scheduled for test installation aboard the Maersk Cardiff late this summer.
“As a front-runner in the pursuit of green technologies, we are interested in testing the new EGR boiler aboard the Maersk Cardiff in order to hopefully demonstrate its promising potential for energy optimization in connection with the existing EGR installation,”
Up to 10% more steam power production
What exactly could the Aalborg XW-HPX achieve if successful? As a producer of service steam, it would provide the same saturated steam as a traditional exhaust gas boiler, though it would be more cost-efficient and easier to install.
Yet a great potential lies in integrating the Aalborg XW-HPX with existing waste heat recovery after the turbocharger, so that it shares a steam drum with the traditional exhaust gas boiler. With the output of the traditional boiler feeding into this drum, the Aalborg XW-HPX would produce extremely high-quality steam with a temperature of 400°C, bringing the waste heat recovery system to a much higher level of efficiency.
“Producing steam of this quality would greatly increase the performance of the steam turbine,” says Nielsen. “To give an indication, we’ve made calculations together with a leading steam turbine supplier. Those calculations put the power generation increase at 7.5-10%, depending on installation factors.”
On the Maersk Cardiff, for example, the additional generated power could be used to cool containers, thereby limiting the fuel consumed by the genset. But if fed into a shaft generator, it could instead increase the efficiency of the propulsion system, saving considerable fuel as a result.
Fuel savings through even slower steaming
Given the higher output, the increased efficiency in waste heat recovery would be interesting for any vessel like the Maersk Cardiff. Yet the Aalborg XW-HPX could prove its worth in still other ways. Most importantly, using it in an integrated boiler system would allow waste heat recovery to occur at lower main engine loads than today – creating the possibility for even slower steaming.
“The Maersk Cardiff has around 20 sister vessels, all with traditional waste heat recovery systems to compare with,” says Nielsen. “With the Aalborg XW-HPX, we should be able to both increase the efficiency and extend the operating hours of waste heat recovery, which would enable slower steaming and a massive fuel savings. That would be reflected not only in a lower fuel bill, but also in a CO2 reduction on top of the NOx abatement.”
“This is perhaps the most exciting prospect of Alfa Laval’s EGR boiler,” says Witt. “If the Aalborg XW-HPX can shift the operating balance for waste heat recovery by even a small percentage, the potential savings for ship owners and operators is enormous.”
Figure 1: Combining Alfa Laval’s Aalborg XW-HPX pressurized EGR boiler with a traditional installation could extend the operating range for waste heat recovery, enabling fuel savings through even slower steaming.
Anne Henningsen - Central Communication Manager
+45 9930 4016
Anne Henningsen - Central Communication Manager
+45 9930 4016